Which of the following series contains nucleophiles only ?

Options

A. `BF_3 , AlCl_3 , NH_3`
B. `RCH_2^(-) , bar(C)N , CH_3CH_2OH`
C. `BF_3,bar(N)H_2,H_2O`
D. `RNH_2,:"CCl"_2H^(-)`

Answer

To determine which series contains nucleophiles only, we need to identify the nature of each species in the given options. Nucleophiles are electron-rich species that can donate electrons, typically characterized by having a negative charge or possessing lone pairs of electrons.

### Step-by-Step Solution:

1. **Understand the Definition of Nucleophiles**:
- Nucleophiles are species that are rich in electrons and can donate electron pairs. They often have a negative charge or possess lone pairs of electrons.

2. **Analyze the First Series: BF3, AlCl3, NH3**:
- **BF3**: Boron trifluoride is electron deficient (only 6 electrons around boron) and acts as an electrophile.
- **AlCl3**: Aluminum chloride is also electron deficient and acts as an electrophile.
- **NH3**: Ammonia has a lone pair of electrons and can act as a nucleophile.
- **Conclusion**: This series contains both nucleophiles (NH3) and electrophiles (BF3 and AlCl3). Therefore, it does not contain nucleophiles only.

3. **Analyze the Second Series: RCH2-, CN-, CH3CH2OH**:
- **RCH2-**: This species has a negative charge, making it an electron-rich nucleophile.
- **CN-**: The cyanide ion also has a negative charge and is a strong nucleophile.
- **CH3CH2OH**: Ethanol has an oxygen atom with two lone pairs, which can be donated, making it a nucleophile.
- **Conclusion**: All three species in this series are nucleophiles.

4. **Analyze the Third Series: RNH2, CCl2**:
- **RNH2**: This amine has a lone pair on nitrogen and can act as a nucleophile.
- **CCl2**: Dichloromethane has only 6 electrons around carbon and is electron deficient, thus acting as an electrophile.
- **Conclusion**: This series contains both nucleophiles (RNH2) and electrophiles (CCl2). Therefore, it does not contain nucleophiles only.

5. **Final Conclusion**:
- The only series that contains nucleophiles only is the second series: **RCH2-, CN-, CH3CH2OH**.

### Answer:
The correct answer is option 2: RCH2-, CN-, CH3CH2OH.